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Mercury Rises With Summer Heat

Ryerson University researcher Julia Lu. (Ryerson University/Dave Upham) Smog is made up of an array of air pollutants, including mercury. One Ryerson University researcher has found that summer is the peak season for this atmospheric toxin, and that higher levels of mercury species exist in the urban atmosphere as compared to rural regions.

One of many contributing poor air factors, mercury is well-known for its toxic effects on the environment and human health. Airborne mercury’s greatest threat is that it will settle into the surface environment and be converted into the much more toxic organomercury species, which can be accumulated and magnified up the food chain, reaching our dinner table through fish and shellfish consumption.

Mercury measurements in the urban atmosphere have been very limited in contrast to rural and remote areas. Julia Lu, an associate professor in Ryerson’s Department of Chemistry and Biology, and her then-graduate students Xinjie Song and Irene Cheng mounted specialized equipment – including air sampling units and a meteorological station – atop a three-storey building on Ryerson’s campus in downtown Toronto.

From there, the team simultaneously measured three types of mercury: atmospheric gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and mercury associated with particles with sizes less than 2.5 micrometers.

In addition to finding higher mercury levels in urban areas, the team discovered those levels seemed to be affected by human-produced emissions, rather than chemical and photochemical reactions in the environment. The amount of GEM spiked in June. Lu says this is a concern because GEM stays in the atmosphere longer and travels further than its chemical counterparts. The result, she believes, is a global-scale problem.

“Sometimes the spikes were as high as what you would find near point sources of mercury,” says Lu, citing coal-powered and metal-processing plants as examples. “We need to further our understanding of how cities contribute to the mercury problem. And it’s not just GEM that requires attention. Other forms of mercury stay in the atmosphere for a shorter duration and therefore negatively impact local and regional areas.”

As next steps, Lu is working to pinpoint sources of mercury in the urban environment. To help accomplish her objective, she has moved her measurement equipment to the top of a taller building on campus and has outfitted a car that will drive around and measure mercury at street-level. A group of over 10 Ryerson researchers are also developing a weather network that is trying to figure out air-flow patterns in the city.

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